About Rationally Speaking

Rationally Speaking is a blog maintained by Prof. Massimo Pigliucci, a philosopher at the City University of New York. The blog reflects the Enlightenment figure Marquis de Condorcet's idea of what a public intellectual (yes, we know, that's such a bad word) ought to be: someone who devotes himself to "the tracking down of prejudices in the hiding places where priests, the schools, the government, and all long-established institutions had gathered and protected them." You're welcome. Please notice that the contents of this blog can be reprinted under the standard Creative Commons license.

Friday, June 29, 2012

Enjoying natural selection on multiple levels

Normally, this would not be an occasion worthy of comment. The best way to distinguish between Professor Dawkins’ waking and sleeping states is probably on the basis of how contentious he is at a given time. Nevertheless, I’m compelled to say something for two reasons. First, this particular fight happens to be taking place right in my proverbial (and professional) wheelhouse; second, I’ve just finished my annual re-reading of Michael Crichton’s Jurassic Park duology.

That last bit requires some explanation, I know. As I mentioned in my last post, Crichton spent most of his later career playing the role of anti-establishment gadfly. For The Lost World, his sequel to Jurassic Park, he set his sights against the theory of natural selection. Indeed, the centerpiece of the book—almost literally, coming precisely halfway through the page count—is a chapter entitled “Problems of Evolution,” wherein Crichton asked the following about the evolution of human intelligence:

“... where does natural selection act? Does it act on the body … on the developmental sequence … on social behavior … Or does it act everywhere all at once—on bodies, on development, and on social behavior?”

This is an issue known to philosophers of biology as the “levels-of-selection problem” (I’ll abbreviate it as LOS hereafter). Biologists don’t have a clear answer to Crichton’s question, and so he took it to be the case that the theory of natural selection is deeply flawed. But Crichton missed an important point: that LOS is a philosophical rather than biological problem.

Professor Dawkins’ newest fight is about LOS; as it happens, so too is my PhD thesis.* I’m therefore going to take this opportunity to summarize the debate and to show that we do have decent answers to Crichton’s question—so long as we ask those questions in the right context.

Let’s start with a big question. What exactly does the theory of natural selection say, and why is LOS a problem?

There’s a reason that Thomas Henry Huxley (AKA “Darwin’s Bulldog”) responded to the publication of The Origin of Species with the exclamation, “How stupid not to have thought of that!” The reason is that the theory is, very broadly speaking, incredibly simple. It says that individuals that are better equipped for survival in their environments will leave more offspring in a population than worse-equipped individuals, and so each subsequent generation will see a greater proportion of beneficial traits in the population—and this spread of traits is evolution.

More specifically, evolution requires three things: first, that there is variability between the individuals in a population; second, that the variations can be inherited by individuals in the population’s next generation; third, that there is a consistent reason that individuals with one kind of variation leave more offspring than individuals with a different kind of variation. We can call these the requirements of variability, heritability, and differential reproduction. We can imagine these requirements combining into a sort of informal formula for evolution:

In this formula, x is a variable that stands for the individual and y is a variable that stands for the population. Bottom line: if a variable trait benefits most individuals x that have that variation, then you’ll eventually (over multiple generations) see that variation spread to most of a later population y.

To hear Darwin tell it, the correct answer to Crichton’s question is “the body” (as Crichton put it), since whole organisms benefit from their advantageous variations. To wit: tigers have stripes because any individual tiger with stripes—as opposed to one with, say, spots—will (all else being equal) blend in better with its grassy surroundings, thus giving it a better chance of ambushing its prey and surviving long enough to leave lots of tiger babies. This works as an explanation of most organisms’ traits, but there was one trait that always defied Darwin’s explanation: altruistic behavior.

By definition, altruistic behavior—that is, being helpful—benefits organisms other than the one that behaves altruistically. I spend a lot of time helping to care for my infant nephew; that’s time that I could be spending, say, going out on dates that might eventually secure me a child of my own. Helping to care for my nephew benefits him, but it hurts me (evolutionarily speaking). The impulse to care for nieces and nephews should therefore be rare among humans. It’s not. Why not? Cui bono?

If you know of Dawkins at all, then the odds are slightly better than even that you know something about his response to the altruism problem. The so-called “selfish gene” theory, technically known as gene selection, is an elaboration of work done by W.D. Hamilton and G.C. Williams on a phenomenon known as “kin selection.” Kin selection is predicated on the idea that the impulse I feel to care for my nephew is stronger than the impulse I feel to care for (say) my neighbor’s nephew. I know that my nephew is my sister’s son, and that my sister and I were born of the same parents; I therefore know that he carries 50% of my sister’s genetic alleles, and that there’s a 50% chance that any one of my sister’s alleles is one that I also carry. For any one of my nephew’s alleles, then, there’s a 25% chance that I also carry that allele. If I care for my nephew, then my genes have a one in four chance of helping themselves; if I care for my neighbor’s nephew, the odds are much, much lower. Gene selectionists therefore argue that genes are the individuals who benefit in the process of natural selection. Hence Dawkins’ famous claim that organisms are “gigantic lumbering robots” for carrying genes around: I have an impulse to care for my nephew because it helps (some of) my genes, even though it hurts me as a whole.

In 2010, E.O. Wilson and two collaborators wrote an article in Nature attacking the viability of kin selection. We won’t get into the details of their mathematical argument; the bottom line is that things rarely work out so neatly as “my nephew has half of my sister’s genetic alleles and she has half of mine,” and the complexities ultimately call into question the idea that gene selection can explain altruistic behavior. In his newest book and a recent New York Times “Stone” column (interestingly, a philosophy blog!), Wilson proposes an alternative that he calls “multi-level selection.” His account is so called because Wilson believes that nature sometimes selects genes, sometimes selects organisms, and sometimes selects groups—and that the latter option is the one that explains altruism. It was this claim that prompted Dawkins’ scathing review of Wilson’s book, linked in the first paragraph. Undermining the very foundation of Dawkins’ account of selection probably had something to do with it, too.

Group selection says that I may not benefit from caring for my nephew, but my family does, and if my family prospers then so too will I. Altruistic behavior evolves in organisms that develop strong social bonds because benefit ultimately comes back to the altruistic organism through those social bonds. Groups maintained by social ties will therefore be “individuals” that nature can select.

To summarize: LOS is a debate over what gets plugged into x in our evolution formula. Darwin said x=organisms; Dawkins says x=genes; Wilson says x=social groups. (And Crichton says that the spread of possible answers makes the formula wrong, which is about as valid an argument as saying that the equation “2x=y” is wrong because there are just so many numbers that can fit into each variable.)

Between Dawkins and Wilson, each side of the LOS debate gets things right and each side of the debate gets things wrong. We’ll see how by asking another big question: why is there a theory of natural selection?

Darwin once wrote that “all observation must be for or against some view if it is to be of any service.” Recognizing what natural selection stands against should therefore be useful towards recognizing what natural selection stands for. Remember creationism? How about intelligent design? Natural selection provides a (vastly superior) alternative to these theories in explaining why organisms seem so well-adapted to their ways of living; it is an answer to what we might call the design question.

To date, gene selection has provided an astoundingly successful answer to the design question. In addition to explaining altruism, it also explains things like why tigers have stripes: after all, traits like stripes are coded (at least in part) by genes, and so selection of tigers with stripes is also selection of the genes for stripes in tigers. Gene selectionists like Dawkins argue that their account works better than organism-level selection because it explains more, and this seems very largely correct.

Group selection, by contrast, doesn’t do as well at answering the design question, because plugging “social groups” into x raises a number of problems. Let’s assume that my family does benefit from my altruism. Cui bono? Maybe my nephew learns the value of altruism and behaves similarly towards his nephew. My nephew therefore has the altruistic impulse; what sense does it make to say that my family has it? The family is altruistic only if it has individual organisms that are altruistic. Doesn’t that mean that it’s really the organisms that benefit? Groups aren’t coherent individuals in the same sense as organisms or genes, and so it’s much more difficult to say that they have beneficial traits. Without beneficial traits, there’s no evolution formula. Again, Dawkins is very largely correct on this count.

Still, it does seem that group selection is at least theoretically coherent. It may work; what does it work for?

As it turns out, the design question is not the only one that the theory of natural selection is meant to answer. Organisms are well-adapted to their environments, yes, but there’s also the fact that organisms in different species are well-adapted to a very wide variety of different environments. Why? This is what we’ll call the diversity question.

As it turns out, group selection may provide a much more direct answer to the diversity question than does gene selection. Understanding why requires that we understand extinction.

Diversity requires extinction. Tigers are well-adapted to jungle hunting and lions are well-adapted to savannah hunting, but why aren’t there big cats that hunt in both the jungle and the savannah? Natural selection predicts that this hypothetical intermediary group once existed, but went extinct; since the intermediary no longer links the tiger and lion groups, those groups are now distinct species.

Extinction is not random. Certain traits—amount of genetic variability, population size, etc.—have a very strong influence on which species go extinct. But take notice: these are traits of groups, not organisms or genes. In fact, gene selection has a difficult time explaining diversity: it can explain why there are feline jungle hunters and feline savannah hunters, but not so much why there aren’t any remaining feline part-timers that hunt in both. On this point, Wilson is correct: a multilevel account of selection can draw on gene selection to answer the design question and group selection to answer the diversity question, and so benefits from the strengths of both accounts.

This has been an admittedly broad sketch of an overview of a deeply nuanced topic, and I’m sure that more than a few readers inclined towards evolutionary biology are now engaged in the harmful act of banging their heads against a wall. (Some of them may be on my dissertation committee.) Sorry: it’s tough to capture nuance in a blog post.

Nevertheless, I hope all readers can take this much away: the question of where natural selection works is one that depends on a philosophical question. What is an individual in biology? We’re used to thinking in terms of organisms—if we don’t count humans as individuals, then what would we count?—but we have compelling reasons to think of entities at other levels of organization as individuals, too. Are my genetic alleles individuals with “interests” distinct from mine? Why should I be able to call the group Homo sapiens a biological individual, but deny that individuality to the group “Finkelman family”? It’s difficult to imagine what sort of empirical data could decide these questions, and this is where the philosopher makes his living.

* If I make fewer attempts at humor here than I normally do, it’s only because this is obviously the most important problem that anyone can possibly work on, under any circumstances, and it must be treated with all due severity.

37 comments:

You've omitted the Lamarckian and Baldwinian contentions that selection is primarily driven by the organism's reaction to its significantly changing experience, and that by the continual process of trial and error, it learns different adaptive behaviors which in turn add selective pressures to readjust the shapes of the physical apparatus that enables the behaviors to fulfill their newly anticipated purposes. More or less.Dawkins, by the way, doesn't believe that purpose of any sort play a role in evolution, but he's not the only one.

In the great apes, we have not only learning to consider, but also, in some cases, cultural evolution. It's hardly a stretch to invoke the Baldwin effect (I omit Roy's "primarily" in characterizing it).

Much of "natural genetic engineering" — phenomena that James Shapiro rightly emphasizes, but wrongly anthropomorphizes — can be accounted for only by organism-level selection. For instance, it's a reasonable guess that genome shuffling in stressed bacteria originated as cellular malfunction. When an organism generates many offspring, and the "selection pressure" is high, a risky (high variance, low mean fitness) reproductive strategy can yield more offspring, on average, than a conservative strategy. (There's good theory to back this up.) I'm suggesting that cells have evolved to "mess up" their genomes better (in ways that are less likely to be lethal), when stressed, than they used to.

Cultural evolution is "primarily" the result of the culture having accelerated the spread of lessons taken from its individual participants' experiences. It shares the learning process among the other participants. More likely these are kin who may have learned these lessons together. It has little to do with altruism, or love among the genes. It has a lot to do with evolution of all species that share some form of inter communicative culture. Bacteria communicate continuously, quorum sensing couldn't happen otherwise.Further, Shapiro doesn't anthropomorphize at all. He recognizes life's common behavioral strategies and characteristics.

The basis of altruism may be the home, the body of the parents intially, mainly the mother, the attachments from which we grow and to which we return, it seems quite a practical cycle, not requiring deep philosophical analysis but requiring analysis of the psychological connection to that biological cycle.

The basis of biology is two-fold, but we have only seen it from one way to date. Selection is open and non-predictive, except to say that traits of all kinds will survive, first if they happen, and then if they can. What can? That's crystal ball stuff based on past patterns of survival, but why go to step 2 before fully exploring step 1?

A reason for Dawkin's convergent "trades" might not be that selection (whatever it may be) very strongly favors particular traits, but that DNA has a limited chemical environment and layered landscape with which to construct anatomies. Stop at step 1, and examine the limits to the available chamicals, and their specific capacities with which DNA "might" in the first place mutate something constructable.

I say "might", because mutation is still considered random, in the traditional view of DNA to function rather than function to DNA, but new research into RNA's role in Epigentics is open to tendencies to mutations. I would simply say we are arrogant if we assume we understand the myriad affinities that operate between the elements of the periodic table to form even the compounds we have studied in detail. Chemistry is almost art.

In any event, even if mutations are "random" (even despite prexisting affinities) the chemical landscape itself will limit what is possible to construct, and over billions of years what catches on may be what resembles the environment. I propose that the human anatomy, for example, may be the chemical ambodiment of the landscape (gasses, liquids, minerals, and solids, for example as basics), and microbiology must understand how DNA fashions anatomies from those chemicals, and the limits to its strongly predictive potential. That's your new research program Massimo.

There is an interesting debate in the edge website about this. Steven Pinker wrote an essay against group selection and others have commented on it. here: http://edge.org/conversation/the-false-allure-of-group-selection

Pinker is a staunch neo-Darwinist, one of the more intelligent, but when he says things like this, you have to wonder: "Granted, it's often convenient to speak about selection at the level of individuals, because it's the fate of individuals (and their kin) in the world of cause and effect which determines the fate of their genes. Nonetheless, it's the genes themselves that are replicated over generations and are thus the targets of selection and the ultimate beneficiaries of adaptations".He doesn't seem to get that the individuals produce their genes with slightly different traits to serve an evolutionary purpose. We survived by intelligent reactions to the randomness of nature, and we have learned to program our genes accordingly. As multicellular organisms, we engineer our changes with help from that process, where single cell organisms effectively redesign themselves before they make their copies. Etc., etc.But then all these Dawkinsists are marvelous rationalizers. I'm less marvelous but I try.

Roy, I don't think Pinker will dispute what you said, but the point he is trying to make is that the genes are the replicators not the bodies that carry them. When people (or any other organism) reproduce sexually, the offspring is not a replica of the parent, only the genes.

Actually the offspring is not a replica of either the genes or the parent. So when I said "copies" it was probably the wrong word to use. The offspring results from instructions carried by the sperm that wins the race, and each sperm seems to carry slightly different instructions, DNA, RNA or otherwise. As do the eggs of the female apparently. So the child is not a replicate of any parent, but a blend of their predominate traits. Mendel's laws seem to apply here, and they have seemed over time to be reliable. (Not that I ever really understood them.)And to say that the offspring is a replica of its genes over generations is just wrong.The information that genes carry is never exactly the same over time, and genes are nothing without their information.

It's that thinking that got me interested in biology, when my brother a year ahead in high school said flat out "we select oursleves!". Took me a while to get what he meant, but it might be possible that the chemical environment of the cell at mutation is more complex than providing a theatre for mere random chance.

This is how we take advantage of random choice:http://biology.clc.uc.edu/courses/bio104/meiosis.htmMeiosis II"Interestingly, because the homologous pairs line up during Metaphase I, there is a 50:50 chance of which one of each pair will go to each of the poles of the cell (like flipping a coin, where you can get either heads or tails). Therefore, in humans with 23 pairs of chromosomes, a gamete (egg or sperm) could have 223 or 8,388,604 possible combinations of chromosomes from that parent. Any couple could have 223 × 223 or 70,368,744,177,644 (70 trillion) different possible children, based just on the number of chromosomes, not considering the actual genes on those chromosomes. Thus, the chance of two siblings being exactly identical would be 1 in 70 trillion. In addition, something called crossingover, in which the two homologous chromosomes of a pair exchange equal segments during synapsis in Meiosis I, can add further variation to an individual’s genetic make-up."Somebody who knows Pinker should remind him of that.

I think what you are getting at is the difference between the species and the individual. Traits are constrained by the universal process of reproduction, involving genetic scrabble, so it would be the framework of that universal process (chromosome and gene behavior), which is a species process shared with other species across evolution.

The genes that are scrabble in that species process would be scrabble for the purposes of the individual produced by that process. Individuals are churned out with genes intact, rather than genes scabbled to hopefully produce a workable individual. The individual of the species, by a species process, is guaranteed by the controlled scrabbling of genes. I favor the individual over the gene on that analysis, and that the individual would be the point of the species, being churned out by the species process.

Imagine a framwork of chromsomes carrying genes as a process that scrabbles the genes as you describe. If genes were the level of selection, why scrabble them?

If genes have priority, there should be a way for them to prioritize, when in fact they seem to fit in all sorts of ways to make individuals, and the individual survives or not along with all of the genes.

Thus individuals have priority both as the entity that survives as holus bolus genes, and because the genes are just scrabble in that process, without any known priority.

Genes aren't scrabbled. They are diversified for a purpose. It's an intelligent adaptation (or preadaptation) process that improves the odds of the members of the next generation to survive as a group of diverse individuals, whether it's a family group, or a group of families. Environmental changes are not predictable with accuracy, but the need to be prepared for dealing with a range of changes is something every species has learned.

I would say they are scrabbled. I don't mean scrambled, because the combinations that come out in the individual might have more survival value in that arrangement, as if spelling out more useful words than random letters.

But they are rearranged in unpredictable ways. As you say, the basis is a species process to churn out individuals that share a spectrum of genes across a group, enhancing survival chances. But that is static.

Development must spring from novelty within the group, by one or more individuals whose genes mutate and reproduce within the group. If you ask what is selected, I would say the individuals that have those new genes are from a species process to churn out individuals to be selected.

There is a possibility that individuals will add value to the group by mutation. It gets back to individuals in the selection of a species process. One mate is needed to reproduce a new trait, but clearly chances are increased all around if there is widespread group sharing of the new addition.

I don't understand where you are coming from either. It began with your discussion of the process pre selection, which I am trying to outline as a process for more or less random mixing, apparently an accident by your definition. Mutation is also generally considered an accident, but that's a separate issue as you haven't mentioned it at all, merely the circular process of mixing genes within a species. So I brought in mutation to make it more real. It's quite logical.

Intelligent responses to the accidents of random mixing or mutation? That makes no sense to me at all. Intelligence is as given by mutation as long as it can survive by whatever means, and if those cards are dealt randomly then so be it. But I doubt it for particular reasons not yet stated, rather than blind faith in a purpose of intelligence.

Random mixing done for an intelligent purpose is no accident. Mutations don't give intelligence, unless they are intelligently directed to. Neo-Darwinians think otherwise, but your rather weird understanding of any of the current theories isn't supported by any of them.

You are back to intelligent purpose again as your fundamental condition, which is nonsense under any current theory you might like to apply. My explanation is structurally sound, although you can make sweeping unsubstantiated summaries such as 'weird' if you like. That's not an argument.

In my theory, intelligence is both from mutation to produce the '747' (unlikely) and selection to allow it to continue (obvious). At least I have clearly set the scene for my theory, rather than falling into a mantra. But I'm not going to bother with that right now.

Clearly the 747 argument applies despite selection for intelligence or anything else, as the next mutation could be anything. Accumulated tiny anythings becoming a highly specific something would take forever, literally, even if selected upon each mutation arising to eliminate duds. That's a clue for you, it's back to the drawing board.

In terms of current theory yours is nonesense, yes. Mine is parallel, as it provides the mutational level, where the problem lies. You understand purpose at the selection level, like everyone else who proposes purpose, as that is the level on which biology is investigated.

The penny has not dropped for anyone that the mutational level is yet to be defined, because we comfortably explore the broad limits of selection and revere Darwin, thinking there is nothing more. It's a common human tendency to conform, and our numbers are low anyway as 90% of the world is spiritual and not really on board.

See the 4th post in this blog for an outline of where my theory fits in. I have been arguing with knowledge of your absent argument and my real argument, although you have suspected I have no real argument, which would be illogical without some investigation, so there is an opportunity for you.

For me, your argumentation breaks down the moment you turn to the diversity question, and that is because to me it simply does not make any sense to call population sizes and amounts of genetic variability "traits".

The first problem is, a trait of whom? Of the species perhaps? So you appear to assume that the groups of groups selection are species. That would mean we are thinking in terms of various species competing against each other, with some of them producing more descendent species than others, and some being selected against because of their traits. That is strange right there.

First, unless they really have no genetic variability, species can react to selective pressure by changing. A gene copy in the gene-centered view of evolution or an individual cannot do that, so it makes much more sense to see them as the objects of evolution. It is also strange to consider a species more successful because it has produced more offspring species. Speciation often happens simply by fragmentation, i.e. insufficient gene flow between increasingly isolated populations.

Imagine the earth is getting warmer for a few hundred thousand years, and one species cannot live in the lowlands any more but only on six isolated mountain ranges. So over time, merely through genetic drift, it fragments into six reproductively isolated species, but each of them is now genetically impoverished and has such a low population size that they are all very vulnerable. It would have been better for their chances of survival if they had all remained one species. Again, this is not a problem for a gene- or individual-centered view: the more copies there are of either, the better the chances that some of them will still be around in the distant future.

Group selection really does not seem very coherent to me.

Roy,

Oh I would loooove for you to tell me how we can "program our genes accordingly". A person very dear to me has a genetic disorder that endangers her life, and they would just have to tell all their cells to change one nucleic acid. So: how do you do that? In case it helps, the "evolutionary purpose" to be "served" here is called "not dying before age 20". I am waiting.

We do not know the cause of any specific mutations that survive, and it is convenient to say they are random as we choose to see DNA to functions without knowing enough about DNA. The role of the chemical environment of the cells at mutation is still being explored.

Say, a trait is a gene, and genes are on chromosomes that obey strict laws within and between species to mix genes robustly for new individuals. Say, the individual survives because just one of those genes happens to work at a crucial moment. Has the gene or the individual been selected if that individual finds a mate and reproduces it? Clearly the individual with the gene has survived, so how do we prioritize? I would only do so because the individual is part of a species process that is a framework to collect and reproduce genes of intact individuals. That process has priority, and the individual is its flagship, complete with genes.

So you think that accidents will reprogram our genes better than our internal reactions to experience? Good for you. Either way, it won't happen in one generation, so that was a rather dumb question. What we can do, however, is intelligently reprogram some of our genes experimentally, because we have scientists who have the evolved level of intelligence to learn to do that.

As to group selection, we have species that cooperate with other species as well as those that prey on each other. There are no species that come without at least a family group. Even the more solitary sharks form attacking groups. (I'm sure you'll tell me of exceptions, but what the hell.) If they didn't teach each other what they've learned and cooperate at some point as a group in applying these lessons, none in the end would survive to evolve. It's really that simple.

@Kei,If groups weren't formed to teach their members what to do and how to do it to survive, then no life forms would have survived. They don't learn the myriad of things they have to learn by their own experience when their competitors have had the advantage of their cultures.Inclusive fitness is about success by cooperative social behavior. But it should also be cognizant of the effects of that group learning experience on the evolution over time of its members. Groups also develop strategies of how best to react to accidents. Accidents don't offer strategies without the assistance of the group intelligence.Cells react to the bodies' experience intelligently. But that experience in turn depends on other levels of intelligence in that same body as well as in the overall group. That's one way of looking at multi-level pressures in evolution.

Meh - The problem here is that group selection is composed of gene selection at a lower level. Much like a bridge can be described as a collection of girders or as a collection of atoms. The question is not "which is true?" but "which level is more useful for a given question?".

So is there a domain where group selection is more useful or are we better off going ahead and making the reduction to the gene level? I don't know but I'm not terribly impressed with the tigers and lions example. Maybe the cichlids of lake Victoria would make the point better.

Level of selection could mean several things. (1.) A unit or target of selection or (2.) a level of biological organisation that structures fitness of targets/units of selection. Elisabeth A. Lloyd has sorted these ambiguities out a long time ago. I wonder why they still exist. When group structure and dynamics is said to constitute a level of selection, AFAIK, 2. is meant not 1.

Selection is open to whatever mutated trait survives, and whether a group of some extent is required for individual traits to survive will vary (beyond one partner to satisfactorily reproduce the trait), so it is one of the factors falling under the general umbrella.

Natural selection operates on entities composed from lesser things that are related by non linear interactions. Both mutual profit and other kinds of unbalanced interactions such as predation make a mathematics compatible with natural selection on the whole combination.

The specialization of individuals beyond a single bell curve is indeed evidence of natural selection on groups. Male and female is the only evidence needed to establish the phenomenon.